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Extracting optical properties of turbid media using radially and spectrally resolved diffuse reflectance JONATHAN MALSANA,B, RAJAN GURJARA, DAVID WOLFA, AND KARTHIK VISHWANATHA; ARADIATION MONITORING DEVICES (RMD), INC., WATERTOWN, MA; BNORTHEASTERN UNIVERSITY, BOSTON, MA INTRODUCTION AND BACKGROUND • • • Measurement of optical absorption (μa) and scattering (μs) properties provide information of medical importance: • Blood oxygenation level1 • Photosensitive drug concentrations2 • Early signs of cancer3 Desire a non-invasive, inexpensive, portable method to determine optical properties of any sample Spectrally based Diffuse Reflectance Spectroscopy has been shown to do this, however it requires that all possible absorbers in the sample be known4 EXPERIMENTAL METHODS PHANTOM PREPARATION • Diffuse Reflectance Spectroscopy (DRS) measures diffuse light remitted from a surface after it has undergone multiple scattering events inside the sample • A probe consisting of a source, shown by the black arrows below, and detectors, shown by the gray arrows, is placed on the surface in question to make measurements • Radially Resolved DRS (RRDR), demonstrated on left, uses the intensity at multiple source-detector separations to find a unique set of optical properties that fits every point • Spectrally Resolved DRS (SRDR), demonstrated on right, uses the reflectance measurements across a wide spectra, to scale input absorption shapes to fit the entire spectra at once • Requires the use of a reference measurement with known optical properties for calibration • • • • • Solid Phantom contained unknown optical properties Created liquid phantom set with known amounts of hemoglobin, polystyrene microspheres and water allowing for calculation of optical properties Table below shows the composition of each absorber along with expected optical properties Performed RRDR measurements on solid phantom and fit to theoretical data produced by Diffusion Theory5, Modified Diffusion Theory6, and a Scalable Monte Carlo Simulation7, referenced as DT, MDT and MC respectively Checked accuracy by feeding as reference to SRDR model used to derive the known properties of the liquid phantom set Phantom µa range Mean µa Number (cm-1) (cm-1) 1 0.01-0.82 0.34 2 0.12-1.02 0.42 3 0.16-1.39 0.57 4 0.21-1.75 0.72 5 0.25-2.09 0.86 6 0.28-2.42 1.00 7 0.32-2.74 1.13 8 0.42-3.61 1.49 Experimental setup- Broadband halogen lamp on left, USB spectrometer on top, and probe on bottom RRDR- Shows source and detector locations, with experimentally gather reflectance measurements at each detector location SRDR- Contains one source and one detector, with example photon paths for various wavelengths of light • • The RRDR derived absorption and scattering spectra for each method is on the right The mean extracted vs mean expected optical properties for each phantom of the Liquid Phantom set is plotted, where the legend corresponds to which set of RRDR phantoms was used • Black line is 1-1 expected vs. extracted • Gray lines show 10% error The teal diamonds show what happened when a liquid phantom was used as reference µs range (cm-1) 60.8-155.5 60.1-153.7 58.8-150.3 57.5-147.0 56.3-143.9 55.1-140.9 54.0-138.0 50.9-130.0 Mean µs (cm-1) 99.9 98.8 96.6 94.5 92.5 90.6 88.7 83.6 Scatterer Spheres (mL) 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Total Volume (mL) 43.5 44.0 45.0 46.0 47.0 48.0 49.0 52.0 Table demonstrates the contents of each of the liquid phantoms used along with average range and mean value for each optical property RESULTS • Absorber Stock (mL) 2.0 2.5 3.5 4.5 5.5 6.5 7.5 10.5 CONCLUSION • The Radially Resolved method is not capable of producing accurate optical properties However, it does produce the spectral shape of absorption The Spectrally Resolved method requires the spectral shape of absorption, which can be taken from any sample using RRDR By combining both methods, the optical properties of any unknown sample can be collected • • SRDR • REFERENCES 1. • • • Absorption spectrums from RRDR methods were used as the absorber shape input to the SRDR method Using a liquid phantom as reference, the SRDR method predicted the following absorption and scattering spectra, seen on the right, for the corresponding RRDR methods When tested as in the same way as RRDR derived properties, the percent errors between expected and extracted can be seen in the table on the right Absorption SRDR Scattering DT MDT MC Liquid Mean 3.56 3.60 3.48 3.36 2. S.D. 5.50 5.64 5.19 4.74 3. Mean 6.96 6.52 7.54 6.84 4. S.D. 5.80 5.37 6.18 5.91 5. 6. 7. • • • Built second liquid phantom set using milk and drops of blue, green, yellow and red food dyes Then used the solid phantom as reference, with both the RRDRderived and SRDR-derived properties, to fit each phantom in the set using the SRDR-model The derived number of drops from each model along with the control can be seen in the bar graphs to the right Solonenko, M., Cheung, R., Busch, T. M., Kachur, A., Griffin, G. M., Vulcan, T., Zhu, T. C., Wang, H. W., Hahn, S. M., and Yodh, A. G., "In vivo reflectance measurement of optical properties, blood oxygenation and motexafin lutetium uptake in canine large bowels, kidneys and prostates", Phys Med Biol, 47 (2002), 857-73. Wilson, B. C., and Patterson, M. S., "The physics, biophysics and technology of photodynamic therapy", Phys Med Biol, 53 (2008), R61-109. Brown, J. Q., Vishwanath, K., Palmer, G. M., and Ramanujam, N., "Advances in quantitative uvvisible spectroscopy for clinical and pre-clinical application in cancer", Curr Opin Biotechnol, 20 (2009), 119-31. Bender, J. E., Vishwanath, K., Moore, L. K., Brown, J. Q., Chang, V., Palmer, G. M., and Ramanujam, N., "A robust monte carlo model for the extraction of biological absorption and scattering in vivo", IEEE Trans Biomed Eng, 56 (2009), 960-8. Farrell, T. J., Patterson, M. S., and Wilson, B., "A diffusion theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo", Med Phys, 19 (1992), 879-88. Kienle, A., and Patterson, M. S., "Improved solutions of the steady-state and the time-resolved diffusion equations for reflectance from a semi-infinite turbid medium", J Opt Soc Am A Opt Image Sci Vis, 14 (1997), 246-54. Kienle, A., and Patterson, M. S., "Determination of the optical properties of turbid media from a single monte carlo simulation", Physics in Medicine and Biology, 41 (1996), 2221. ACKNOWLEDGEMENTS This work was supported in part by NIH award R00CA140783 to KV. Radiation Monitoring Devices, Inc. 44 Hunt Street Watertown, MA 02472-4699 www.rmdinc.com Phone: (617) 668-6800